利用波形重定改善近岸與內陸小水體之Envisat測高資料

Improvement of Envisat measurements in coastal oceans and inland small water bodies by waveform retracking

測高衛星提供穩定且長時間的海面觀測數據，可應用於海水面上升和重力異常等研究議題。近年來多人致力於將衛星測高資料應用於近岸與內陸小範圍水體，以提供洪氾淹水災害評估、海岸侵蝕監控或水資源控管等多元應用。然而，近岸與內陸水體應用仍有部分難題需要克服，諸多因素造成測高波形複雜，例如岸邊多變的地形與海水面、改正模型精度較低等。複雜的波形導致難以求得精準之海水面高。因此，本研究欲以新的波形重定技術，改善測高數據之精度與品質。
本研究利用近岸EnviSat RA-2波形觀測數據，以Brown加上高斯模型配合波峰自動偵測進行波形重定，以求得精準之海水面高，並利用沿海潮位站資料及地球重力模型（EGM2008），對波形重定後的海水面高進行精度評估和分析。而內陸小範圍水體部分，本研究利用曾文水庫EnviSat RA-2波形，以小波方法改善現有之波形重定技術，並與傳統水位站資料進行分析比較。

Satellite altimeters provide many kinds of accurate ocean measurements and become an irreplaceable tool to address wide range of scientific questions over the open oceans. In recent years, there are increasing demand for altimeter observations in the non-ocean surfaces, especially in the coastal zone and inland water. However, the accuracy of observations is quickly degenerated as the altimeters are close to coasts or on non-ocean surfaces, due to improper geophysical corrections and complex returned waveforms. In this study, we develop a novel strategy to derive accurate sea surface heights (SSHs) near the Taiwan coasts from Envisat RA-2 waveforms by using the Ocean plus Gaussian Models. We also automatically filter the improper ocean waveforms, and validate the experimental results using tide gauge records and EGM2008. Furthermore, a wavelet-based algorithm is used to retrack the Envisat waveforms in Tsengwen reservoir and Zhoushui river. The retracked water heights are evaluated using water level gauge data.